Question: "Confirmation is the process of obtaining and evaluating a direct communication from a third party in response to a request for information about a particular item affecting financial statement assertions".(aicpa.org). Confirmation requests, if properly designed by the auditor. Accounts receivable confirmations are likely to be more effective for the existence assertion than for the completeness and valuation assertions. So, when obtaining evidence for assertions not adequately addressed by confirmations, auditors should consider other audit procedures to complement confirmation procedures or to be used instead of confirmation procedures. (aicpa.org). During the performance of confirmation procedures, the auditor should maintain control over the confirmation requests and responses. Also, the auditors should maintain communication between the intended recipient and the auditor to minimize the possibility that the results will be biased because of interception and alteration of the confirmation requests or responses.
References: AICPA. The Confirmation Process - aicpa.